Developer details moving email domain from DMARC monitoring to quarantine without breaking mail

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A developer whose app sends invitation, password-reset and alert emails found that a DMARC policy of p=none left the domain open to forged messages, since receivers were told to take no action on failures. Setting up SPF, DKIM and DMARC together required fixing an SPF record that exceeded the ten-lookup limit by one, which was flattened to five lookups. Signing was added to the Nodemailer transport using a private key stored base64-encoded, with the new public key published in DNS before the private key was deployed during rotation. After confirming the key pair matched, the policy was raised to p=quarantine on 12 September, sending failing mail to spam rather than rejecting it. The author chose to hold off on configuring the subdomain policy tag.

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